Mucor Rot—An Emerging Postharvest Disease of Mandarin Fruit Caused by Mucor piriformis and other Mucor spp. in California

In recent years, an emerging, undescribed postharvest disease was observed on mandarin fruit after extended storage in California. We collected decayed mandarin fruit from three citrus packinghouses in the Central Valley of California in 2015 and identified this disease as Mucor rot caused by Mucor spp. Mucor rot occurred in 11 of the 15 grower lots sampled, and the percentage of Mucor rot in the total decayed fruit varied among affected grower lots, ranging from 3.3 to 93.1% with an average of 49.2%. In total, 197 isolates of Mucor spp. were obtained from decayed mandarin fruit and identified based on internal transcribed spacer sequence and morphological characteristics. Of the 197 isolates, 182 (92.4%) were identified as Mucor piriformis, 7 (3.6%) were M. circinelloides (6 M. circinelloides f. lusitanicus and 1 M. circinelloides f. circinelloides), 4 (2%) were M. racemosus f. racemosus, 3 (1.5%) were M. hiemalis, and 1 (0.5%) was M. mucedo. All species grew at 0 and 5°C, except M. circinelloides, which did not grow at 0°C. Mycelial growth was arrested at 27°C for M. piriformis; 35°C for M. racemosus f. racemosus, M. circinelloides f. lusitanicus, M. hiemalis and M. mucedo; and 37°C for M. circinelloides f. circinelloides. Optimal mycelial growth occurred at 20°C for M. piriformis and M. mucedo, 25°C for M. racemosus f. racemosus and M. hiemalis, 27°C for M. circinelloides f. lusitanicus, and 30°C for M. circinelloides f. circinelloides. M. piriformis grew significantly faster than the other four species at 5 and 20°C, and M. mucedo was the slowest in growth among the five species. Sporangiospores of M. piriformis, M. racemosus f. racemosus, and M. hiemalis germinated at both 5 and 20°C. M. circinelloides germinated at 20°C but did not germinate at 5°C after incubation for 48 h. All five Mucor spp. caused decay on mandarin fruit inoculated with the fungi, and the lesion size caused by M. piriformis was significantly larger than that caused by other species at both 5 and 20°C. Our results indicated that Mucor rot in mandarin fruit in California is caused by Mucor spp. consisting of M. piriformis, M. circinelloides, M. racemosus f. racemosus, M. hiemalis, and M. mucedo, with M. piriformis being the dominant and most virulent species. Previously, M. racemosus was reported on citrus. This is the first report of Mucor rot in citrus caused by M. piriformis, M. circinelloides, M. hiemalis, and M. mucedo.

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First Report of Soft Rot on Dendrobium officinale caused by Epicoccum sorghinum in China

Plant Disease ◽

10.1094/pdis-04-21-0866-pdn ◽

2021 ◽

Author(s):

Caiyun Xiao ◽

Rongyu Li ◽

Xingchen Song ◽

Xujun Tian ◽

Qijun Zhao

Keyword(s):

Internal Transcribed Spacer ◽

Elongation Factor ◽

Morphological Characteristics ◽

Reference Value ◽

Soft Rot ◽

Dendrobium Officinale ◽

First Report ◽

Rdna Its ◽

And Control ◽

Internal Transcribed Spacer Rdna

In recent years, soft rot is one of the most serious diseases in the production of Dendrobium officinale. In this study, we took the diseased plants of Dendrobium officinale in Guizhou as samples, through Koch's rule and sequence analysis of rDNA internal transcribed spacer (rDNA-ITS), calmodulin (cmdA), the second largest subunit of RNA polymerase Ⅱ (RPB2), elongation factor EF-1 α and β-tubulin (β-Tub), it was determined that the pathogen of Dendrobium officinale soft rot was sorghum accessory cocci. This is our first report on the soft rot of Dendrobium officinale caused by Epicoccum sorghinum in China. The morphological characteristics of the pathogen shown in the study will have a certain reference value for the prevention and control of the soft rot of Dendrobium officinale in the future.

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First report of Fusarium proliferatum causing stem and root rot on lucky bamboo (Dracaena braunii) in Iraq

Hellenic Plant Protection Journal ◽

10.2478/hppj-2019-0001 ◽

2019 ◽

Vol 12 (1) ◽

pp. 1-5

Author(s):

A.A. Lahuf

Keyword(s):

Ribosomal Dna ◽

Root Rot ◽

Internal Transcribed Spacer ◽

Morphological Characteristics ◽

Its Region ◽

Fusarium Proliferatum ◽

Ornamental Plant ◽

Sequence Analyses ◽

First Report

Summary Lucky bamboo (Dracaena braunii) is a popular ornamental plant in Iraq. Individuals of this plant showing stem and root rot symptoms were observed during a survey conducted from November 2015 to February 2016 in several nurseries in Kerbala province, Iraq. Based on morphological characteristics and sequence analyses of the internal transcribed spacer (ITS) region of the ribosomal DNA (rDNA), the pathogen was identified as Fusarium proliferatum. This is the first report of stem and root rot caused by F. proliferatum on lucky bamboo (D. braunii) in Iraq.

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First Report of Lasiodiplodia pseudotheobromae Causing Stem End Rot of Mango Fruit in Pakistan

Plant Disease ◽

10.1094/pdis-01-21-0099-pdn ◽

2021 ◽

Author(s):

Muhammad Waqar Alam ◽

Arif Malik ◽

Abdul Rehman ◽

Mubeen Sarwar ◽

Tahir Shafeeq ◽

...

Keyword(s):

Disease Incidence ◽

Mangifera Indica ◽

Morphological Characteristics ◽

Aerial Mycelium ◽

Postharvest Disease ◽

Single Spore ◽

Mango Fruit ◽

First Report ◽

Field Samples ◽

Rot Disease

Mango (Mangifera indica L.) is considered a desirable fruit in international markets and is grown throughout tropical and sub-tropical countries around the world (Alemu, 2014). Stem end rot is the most damaging and complex postharvest disease of mango, resulting in losses of up to 40% in Pakistan, which is the leading producer and exporter (Alam et al. 2017). A field survey was conducted in June of 2017 and 2018 in the Rahim Yar Khan and Multan- major mango producing regions of Punjab Province. After mature but unripe mango fruit (cv. Samar Bahisht Chaunsa) were stored at 12°C for 2 weeks to permit ripening, water-soaked, dark brown to purplish black decay began to appear around the stem end portion. The decay gradually enlarged and covered the whole fruit after 7 days. Disease incidence was estimated at 30%. Small pieces (3 to 4 mm2) from the periphery of 15 diseased fruit were surface disinfected with 1% sodium hypochlorite for 2 min, rinsed three times in sterilized distilled water, air dried, and then placed aseptically onto potato dextrose agar (PDA) medium and incubated at 25°C under a 12-h light/dark photoperiod for 7 days. Twelve single-spore isolates with similar morphology were isolated from the infected tissues. Initially the fungus produced thick, fluffy and greyish-white aerial mycelium, that later turned into dark gray colonies. Conidia were unicellular, ellipsoidal, and initially hyaline, but with age became dark brown and developed a central septum. Conidia measured 24.5 to 31.5 × 11.4 to 15.7 µm (n = 60). Conidiophores were inflated at their base with one diaphragm which reduced to conidiogenous cells. Conidiogenous cells were hyaline and cylindrical. On the basis of morphological characteristics, the fungus was tentatively identified as Lasiodiplodia sp., a member of the family Botryosphaeriaceae (Alves et al. 2008). For molecular identification, genomic DNA was extracted from mycelium following the CTAB method. The internal transcribed spacer (ITS) region of rDNA and translation elongation factor 1-alpha (TEF1-α) gene were amplified using ITS1/ITS4 (White et al. 1990) and EF1-728F/EF1-986R primer sets (Carbone and Kohn 1999), respectively. BLASTn searches of sequences revealed 99% to 100% identity with the reference sequences of various Lasiodiplodia pseudotheobromae isolates (GenBank accession nos. MH057189 for ITS; MN638768 for TEF-1a). The sequences were deposited in GenBank (accession nos. MW439318, MW433883 for ITS; and MW463346, MW463347 for TEF-1a). To fulfill Koch’s postulates, a suspension of 105 conidia/ml from a 7-day-old culture of L. pseudotheobromae was used to inoculate fully mature but unripe mango fruit (cv. Samar Bahisht Chaunsa). Fruit were pricked with a sterilized needle to a depth of 4 mm at the stem end portion, injected with 50 μl of the prepared spore suspension (Awa et al. 2012), and stored at 12°C for 3 weeks under 70 to 80% RH. Twenty mango fruit were inoculated, and 10 were inoculated with sterile water only. After 15 days, most fruit showed typical symptoms at the stem end. Reisolations from symptomatic fruit following the procedures described above for isolating and identifying the fungal cultures from infected field samples, consistently yielded a fungus identical to L. pseudotheobromae. Control fruit remained disease-free. Although L. pseudotheobromae was previously reported on several forest and fruit trees (Alves et al. 2008; Awan et al. 2016), this is the first report of the pathogen causing stem end rot disease of mango in Pakistan. This report is important for the new studies aiming at management of stem end rot disease of mango caused by L. pseudotheobromae in Pakistan.

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First Report of Rhizoctonia solani AG-4-HG-II on Garden Pink in Buenos Aires, Argentina

Plant Disease ◽

10.1094/pdis.2001.85.12.1287d ◽

2001 ◽

Vol 85 (12) ◽

pp. 1287-1287

Author(s):

E. R. Wright ◽

M. C. Rivera ◽

K. Asciutto ◽

L. Gasoni

Keyword(s):

Rhizoctonia Solani ◽

Mycelial Growth ◽

Buenos Aires ◽

Morphological Characteristics ◽

Anastomosis Group ◽

Potato Dextrose Agar ◽

Stem Rot ◽

American Phytopathological Society ◽

Basal Stem Rot ◽

First Report

During 2001, basal stem rot, wilt, and plant death were observed on 30% of the plants in a crop of Dianthus plumarius L. ‘Telstar’ in Buenos Aires. Pieces of diseased stems ≈1 cm long were surface-disinfested in 2% NaOCl for 1 min and cultured on 2% potato dextrose agar (PDA), pH 7, at 22 to 24°C. After 7 days, an identical fungus was consistently isolated from pieces of infected tissue. Colonies initially were white, turned brown after 2 to 3 days, and eventually formed irregularly shaped sclerotia. Cultures exhibited morphological characteristics typical of Rhizoctonia solani Kühn (2) and were identified with known anastomosis group tester isolates (1). Positive anastomosis was observed with tester strains of R. solani AG-4-HG-II. One isolate was tested for pathogenicity by placing two pieces of PDA (1 cm2) containing 7-day-old mycelial growth ≈0.5 cm from the base of healthy 2-month-old plants. Control plants were treated with sterile pieces of PDA using the same procedures. Ten replicate plants were used for each treatment. Plants were maintained at 22 to 24°C under 95 to 100% relative humidity and a 12-h light/dark photoperiod. After 7 days, symptoms developed that were similar to those originally observed, and Koch's postulates were satisfied by reisolating the fungus. To our knowledge, this is the first report of R. solani AG4-HG-II causing disease on D. plumarius in Argentina. References: (1) B. Sneh et al. Identification of Rhizoctonia Species. The American Phytopathological Society, St. Paul, MN, 1991. (2) C. C. Tu and J. W. Kimbrough. Mycologia 65:941, 1973.

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First Report of Colletotrichum gloeosporioides Causing Anthracnose of Banana (Musa spp.) in Malaysia

Plant Disease ◽

10.1094/pdis-10-12-0985-pdn ◽

2013 ◽

Vol 97 (7) ◽

pp. 991-991 ◽

Cited By ~ 5

Author(s):

M. A. Intan Sakinah ◽

I. V. Suzianti ◽

Z. Latiffah

Keyword(s):

Morphological Characteristics ◽

Pathogenic Fungi ◽

Culture Collection ◽

Postharvest Disease ◽

Conidial Suspension ◽

First Report ◽

Musa Spp ◽

Initial Symptoms ◽

Dark Green ◽

Average Size

Banana is the second largest cultivated fruit crop in Malaysia, and is cultivated for both the domestic market and also for export. Anthranose is a well-known postharvest disease of banana and with high potential for damaging market value, as infection commonly occurs during storage. Anthracnose symptoms were observed on several varieties of banana such as mas, berangan, awak, nangka, and rastali in the states of Perak and Penang between August and October 2011. Approximately 80% of the fruits became infected with initial symptoms characterized as brown to black spots that later became sunken lesions with orange or salmon-colored conidial masses. Infected tissues (5 × 5 mm) were surface sterilized by dipping in 1% sodium hypochlorite (NaOCl) for 3 to 5 min, rinsed with sterile distilled water, and plated onto potato dextrose agar (PDA). Direct isolation was done by transferring the conidia from conidial masses using an inoculation loop and plating onto PDA. For both methods, the PDA plates were incubated at 27 ± 1°C with cycles of 12 h light and 12 h darkness. Visible growth of mycelium was observed after 4 to 5 days of incubation. Twenty isolates with conidial masses were recovered after 7 days of incubation. The isolates produced grayish white to grayish green and grey to moss dark green colony on PDA, pale orange conidial masses, and fusiform to cylindrical and hyaline conidia with an average size of 15 to 19 × 5 to 6 μm. Appresoria were ovate to obovate, dark brown, and 9 to 15 × 7 to 12 μm and setae were present, slightly swollen at the base, with a tapered apex, and brown. The cultural and morphological characteristics of the isolates were similar to those described for C. gleosporioides (1,2,3). All the C. gloeosporioides isolates were deposited in culture collection at Plant Pathology Lab, University Sains Malaysia. For confirmation of the identity of the isolates, ITS regions were sequenced using ITS4 and ITS5 primers. The isolates were deposited in GenBank with accessions JX163228, JX163231, JX163201, JX163230, JX163215, JX163223, JX163219, JX163202, JX163225, JX163222, JX163206, JX163218, JX163208, JX163209, JX163210, JX431560, JX163212, JX163213, JX431540, and JX431562. The resulting sequences showed 99% to 100% similarity with multiple C. gloeosporioides isolates in GenBank. Pathogenicity tests were conducted using mas, berangan, awak, nangka, and rastali bananas. Fruit surfaces were sterilized with 70% ethanol and wounded using a sterile scalpel. Two inoculation techniques were performed separately: mycelia plug and conidial suspension. Mycelial disc (5 mm) and a drop of 20 μl spore suspension (106 conidia/ml) were prepared from 7-day-old culture and placed on the fruit surface. The inoculated fruits were incubated at 27 ± 1°C for 10 days at 96.1% humidity. After 3 to 4 days of inoculation, brown to black spotted lesions were observed and coalesced to become black sunken lesions. Similar anthracnose symptoms were observed on all banana varieties tested. C. gloeosporioides was reisolated from the anthracnose lesions of all the inoculated fruit in which the cultural and morphological characteristics were the same as the original isolates. To our knowledge, this is the first report of C. gloeosporioides causing anthracnose of Musa spp. in Malaysia. References: (1) P. F. Cannon et al. Mycotaxon 104:189, 2008. (2) J. E. M. Mordue. Glomerella cingulata. CMI Description of Pathogenic Fungi and Bacteria, No. 315. CAB International,1971. (3) H. Prihastuti et al. Fungal Diversity 39:89, 2009.

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First Report of Brown Rot on Plum Caused by Monilia polystroma in China

Plant Disease ◽

10.1094/pdis-94-4-0478a ◽

2010 ◽

Vol 94 (4) ◽

pp. 478-478 ◽

Cited By ~ 20

Author(s):

X. Q. Zhu ◽

L. Y. Guo

Keyword(s):

Ribosomal Rna ◽

Internal Transcribed Spacer ◽

Morphological Characteristics ◽

Brown Rot ◽

Its Region ◽

Apple Orchard ◽

Monilinia Fructigena ◽

First Report ◽

Plant Pathol ◽

Monilia Polystroma

In August 2008, mummies of dwarf sweet plum (Prunus aitianli) fruit covered with grayish, conidial tufts were found in an orchard in Mudanjiang City of Heilongjiang in China. Conidial masses were touched with a sterilized wire loop and streaked onto the surface of water agar (WA) plates. After incubating at 22 ± 2°C for 16 to 24 h, individual germinated spores were picked out with a sterilized scalpel blade under a microscope in a laminar flow cabinet, and transferred to potato dextrose agar (PDA) in petri dishes. Mycelium grew an average of 10.7 mm per day on PDA and formed a white-to-grayish colony with irregular, black stroma 12 days after incubation at 22 ± 2°C under 12-h light/12-h dark. The average size of stroma was 8.19 cm2 per petri dish 37 days after incubation in the dark. The conidia were one-celled, hyaline, lemon-shaped, 15.2 (10.8 to 18.9) × 10.9 (8.3 to 16.3) μm, and arranged in branched monilioid chains on inoculated apples. The PCR products of internal transcribed spacer (ITS) region 1 and 2 and 5.8S gene of the ribosomal RNA amplified with primers ITS1 and ITS4 was directly sequenced in both directions using the PCR primers. The sequence of the Monilia polystroma isolate (GenBank Accession No. GU067539) was identical to the reference isolate of M. polystroma (CBS102686), containing five nucleotides that distinguish it from Monilinia fructigena (1,3). The pathogen was identified as M. polystroma on the basis of morphological characteristics (3) and the sequence of internal transcribed spacer (ITS) region 1 and 2 and 5.8S gene of the ribosomal RNA. Pathogenicity was confirmed by inoculating surface-sterilized, mature plum and apple fruit wounded with a nail, with a mycelial plug (5 mm in diameter) of the fungus at each wound. Fruit treated with plain PDA plugs were used as a control. Inoculated fruits were placed in a sterilized moist chamber at room temperature (23 to 28°C). Fifteen plums and nine apples were used in each of two replicated tests. All inoculated fruit developed typical brown rot symptoms 4 days after inoculation, while the control fruit remained healthy. M. polystroma was reisolated from the inoculated fruit and identified by the above methods. M. polystroma was first reported on apple in Japan (3) and it was recently discovered in an apple orchard in Hungary (2). Although the occurrence of Monilinia fructicola, Monilinia laxa, and Monilinia fructigena (teleomorphs of the three Monilia spp.) in China have been documented, to our knowledge, this is the first report of the occurrence of M. polystroma in China. References: (1) C. E. Fulton et al. Eur. J. Plant Pathol. 105:495, 1999. (2) M. Petróczy and L. Palkovics. Eur. J. Plant Pathol. 125:343, 2009. (3) G. C. M. van Leeuwen et al. Mycol. Res. 106:444, 2002.

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Characterisation and Pathogenicity of Aspergillus tamarii Causing Banana Fruit Rot

Tropical Life Sciences Research ◽

10.21315/tlsr2021.32.3.10 ◽

2021 ◽

Vol 32 (3) ◽

pp. 179-187

Author(s):

Latiffah Zakaria ◽

Yan Yan Chai ◽

Masratul Hawa Mohd ◽

Nur Amalina Kamaruddin ◽

Nurul Farizah Azuddin

Keyword(s):

Internal Transcribed Spacer ◽

Morphological Characteristics ◽

Fruit Rot ◽

Postharvest Disease ◽

Banana Fruit ◽

Aspergillus Tamarii ◽

Pathogenicity Tests ◽

Causal Pathogen ◽

Postharvest Rot ◽

Β Tubulin

Banana fruit rot is a common postharvest disease of the banana fruit. The appearance of rot symptoms on the surface of the fruits reduces the quality and marketability of banana. From rot lesions on banana fruits, three Aspergillus isolates were isolated. Based on morphological characteristics and sequences of Internal Transcribed Spacer, β-tubulin and calmodulin, the isolates were identified as A. tamarii. Pathogenicity tests of the isolates, conducted using mycelial plugs with wounded and unwounded treatments, showed A. tamarii as the pathogen of banana fruit rot. Rot symptoms were highly severe on wounded banana fruits compared to unwounded fruits, and therefore, wounded banana fruits are more susceptible to A. tamarii infection. To the best of our knowledge, this is the first report of A. tamarii as a causal pathogen of banana fruit rot. This study indicated A. tamarii is one of postharvest rot pathogens of banana.

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First Report of Phytophthora nicotianae on Bulb Onion in the United States

Plant Disease ◽

10.1094/pdis-01-11-0048 ◽

2011 ◽

Vol 95 (8) ◽

pp. 1028-1028 ◽

Cited By ~ 3

Author(s):

J. M. French ◽

R. A. Stamler ◽

J. J. Randall ◽

N. P. Goldberg

Keyword(s):

United States ◽

New Mexico ◽

Morphological Characteristics ◽

The United States ◽

Phytophthora Nicotianae ◽

Postharvest Disease ◽

Total Production ◽

First Report ◽

Cell Extracts ◽

Bulb Onion

Phytophthora nicotianae (synonym P. parasitica) Breda de Haan was isolated from recently harvested onion bulbs (Allium cepa) in cold storage from a commercial field in southern New Mexico. Deteriorating, water-soaked tissue from the center of four bulbs was plated onto water agar and incubated at room temperature. After 72 h, cultures of Phytophthora (identified by the presence of coenocytic hyphae and papillate sporangia) were isolated and transferred to V8 agar amended with ampicillin (250 mg/liter), rifampicin (10 mg/liter), and pimaricin (0.2% wt/vol). Isolates were identified as P. nicotianae based on morphological characteristics and DNA analysis. Sporangia were sharply papilliate, noncaducous, and ovoid to spherical. The average sporangium size was 45.9 × 39.9 μm with a length-to-width ratio of 1.15. Clamydospores, both terminal and intercalary, were spherical to ovoid and averaged 37.2 × 35.2 μm (2). PCR from whole-cell extracts was performed on four cultured isolates from the infected onion tissue using previously described primers ITS4 and ITS6, which amplify the 5.8S rDNA and ITS1 and ITS2 internal transcribed spacers (1,4). A band of approximately 890 bp was amplified and directly sequenced (GenBank Accession No. HQ398876). A BLAST search of the NCBI total nucleotide collection revealed a 100% similarity to multiple P. nicotianae isolates previously sequenced (1). To confirm the pathogenicity of the isolates, onion seedlings were inoculated with 25 ml of P. nicotionae zoospore solution (15,000 zoospores/ml). Necrosis of leaf tissue and seedling death was observed 5 days postinoculation. P. nicotianae was reisolated from the infected onion seedlings and the ITS region was sequenced to confirm its identity. P. nicotianae was previously reported in bulb onion from Australia, Taiwan (Formosa), and Zimbabwe (Rhodesia) (2). P. nicotianae was reported on bunching onions (A. fistulosum) in Hawaii in 1989 (3). Onions are an important crop in New Mexico with a total production value of 47 million dollars in 2008 (NM Agriculture Statistics 2008). This discovery of a potentially significant postharvest disease poses a threat to the onion industry in New Mexico. To our knowledge, this is the first report of P. nicotianae in bulb onion in the United States and the first report of P. nicotianae in New Mexico on any crop. References: (1) D. E. L. Cooke and J. M. Duncan. Mycol. Res. 101:667, 1997. (2) D. C. Erwin and O. K. Ribeiro. Page 56 in: Phytophthora Diseases Worldwide. The American Phytopathological Society, St Paul, MN, 1996. (3) R. D. Raabe et al. Information Text Series No. 22. University of Hawaii. Hawaii Inst. Trop. Agric. Human Resources, 1981. (4) T. J. White et al. Page 315 in: PCR Protocols: A Guide to Methods and Applications. M. A. Innis et al., eds. Academic Press, San Diego, 1990.

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First Report of Botrytis pseudocinerea Causing Gray Mold on Blueberry in North America

Plant Disease ◽

10.1094/pdis-06-14-0573-pdn ◽

2014 ◽

Vol 98 (12) ◽

pp. 1743-1743 ◽

Cited By ~ 16

Author(s):

S. Saito ◽

T. J. Michailides ◽

C. L. Xiao

Keyword(s):

North America ◽

Morphological Characteristics ◽

Gray Mold ◽

Postharvest Disease ◽

Conidial Suspension ◽

Internal Transcribed Spacer Region ◽

Genetic Characteristics ◽

First Report ◽

Group I ◽

Pcr Rflp

Botrytis cinerea has previously been shown to consist of two sibling species, referred to as Group I and Group II, that can be differentiated by PCR-RFLP analysis of the Bc-hch gene, a vegetative incompatibility locus (1). Group I has recently been described as a new cryptic species, B. pseudocinerea (4). Gray mold caused by B. cinerea is a major postharvest disease of blueberries in the Central Valley of California. In 2012 and 2013, blueberry fruit were sampled at harvest from various locations in the region and stored at 0 to 1°C for 5 weeks, and fungi were isolated from decayed fruit. In total, 526 isolates of Botrytis spp. were obtained. Genomic DNA was extracted and PCR-RFLP of a fragment of the Bc-hch gene was performed. Four isolates showed the distinctive restriction band pattern associated with Group I (1). The identity of these four isolates was further investigated by sequencing portions of four genes: internal transcribed spacer region, glyceraldehyde-3-phosphate dehydrogenase (G3PDH), heat-shock protein 60 (HSP60), and DNA-dependent RNA polymerase subunit II (RPBII), using the primers described previously (3,4). Sequences were deposited in GenBank (Accession Nos. KJ796643 to 58). BLAST analysis showed that sequences of all four genes for the four isolates were 99.8 to 100% similar to those of B. pseudocinerea. Morphological characteristics of the four blueberry isolates were examined as described previously (4). On potato dextrose agar, colonies were gray; the mycelial growth rate was 26 mm/day at 19°C in the dark. Conidiophores were simple and erect, and conidia were borne in grapelike clusters, one celled, hyaline, elliptical to ovoid, 6.5 to 15.7 × 5.6 to 9.8 μm (average of 7.4 × 10.1 μm). As reported previously, none of the morphological characters was able to differentiate between B. cinerea and B. pseudocinerea (4). To test pathogenicity, freshly harvested organic blueberry fruits were treated with 0.5% sodium hypochlorite for 2 min, rinsed with sterile water, wounded using a sterile needle, and inoculated by placing 1 μl of a conidial suspension (1.0 × 105 spores/ml) from each isolate into the wound with a pipette. Inoculated fruit (10 for each isolate) were incubated at 20°C for 5 days in the dark. Experiments were performed twice. All inoculated fruit developed rot, and no decay was observed on the noninoculated controls. All four isolates of B. pseudocinerea were pathogenic, and the fungus was re-isolated from decayed fruit. B. pseudocinerea isolates are known to be naturally insensitive to fenhexamid (1,4). Sensitivity of the four isolates to fenhexamid was examined in vitro as previously described (4). The EC50 values for fenhexamid for the four isolates ranged from 7.7 to 9.9 μg/ml and isolates were considered resistant to fenhexamid (1,4). Based on the morphological, physiological, and genetic characteristics, the four blueberry isolates were identified as B. pseudocinerea. It appeared that this species was present at very low frequency (0.76%) in blueberry fields in California. Previously, B. pseudocinerea has been reported from French, German, and New Zealand vineyards (1,2,4). To our knowledge, this is the first report of B. pseudocinerea causing gray mold in blueberry in California and in North America. References: (1) E. Fournier et al. Mycologia 95:251, 2003. (2) P. R. Johnston et al. Plant Pathol. 63:888, 2014. (3) M. Staats et al. Mol. Biol. Evol. 22: 333, 2005. (4) A.-S. Walker et al. Phytopathology 101:1433, 2011.

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First report of Geotrichum candidum causing sour rot of peach in China

Plant Disease ◽

10.1094/pdis-02-21-0279-pdn ◽

2021 ◽

Author(s):

Renxiang Lu ◽

Zhe Wang ◽

Yujia Zhai ◽

Runyu Hong ◽

Weixin Jin ◽

...

Keyword(s):

Large Scale ◽

Prunus Persica ◽

Morphological Characteristics ◽

Geotrichum Candidum ◽

Postharvest Disease ◽

Pathogenicity Test ◽

Accession Number ◽

Great Loss ◽

First Report ◽

Sour Rot

Peach (Prunus persica L. Batsch) is one of the most important fruit crops in China (Wang et al. 2011). Yangshan Town of Jiangsu Province is one of the four major peach producing areas in China, with a growing area of 2,000 ha (Tian et al. 2018). During June 2020, a postharvest disease presenting with brown necrosis and rot occurred on peaches in Yangshan Town. The estimated damage was more than 10% of the total harvest. The symptoms included soft rot, and the lesion appeared sunken, accompanied with sour odor and white mycelia. Twelve peaches with representative symptom were sampled for pathogen isolation. Pieces (about 5 mm × 5 mm) from the lesion edge of symptomatic fruits were dissected and surface disinfected (3% NaClO for 10 s and 75% ethanol for 30 s), then rinsed three times with distilled water, dried on sterile filter paper and transferred to Potato Dextrose Agar (PDA) media plates supplemented with 150 ng/mL streptomycin sulfate. The plates were incubated at 28 ℃ for 3 days. Forty-eight isolations were obtained from the plates and isolates were single-spored. All isolates presented white, flat, milky yeast-like colonies with radial mycelia. Hyphae under microscope were septate, branched, disarticulating into arthroconidia measuring 3.39 to 9.27 × 2.05 to 7.71 μm. The morphological characteristics are consistent with Geotrichum candidum (De Hoog et al. 1986). Internal transcribed spacer (ITS) and 18s nuclear ribosomal small subunit (SSU) of the 48 isolates were amplified and sequenced using the primers ITS5/ITS4, and NS1/NS4 for molecular identification (Schoch et al. 2012). The resulted sequences showed no difference among all the isolates. Alignment by blastn showed the sequence of ITS and SSU were 100% (accession number. GQ376093) and 99.7% identical (accession number. KY977411.1) to Geotrichum candidum, respectively. The sequences of ITS (accession number MW493646) and SSU (accession number MW493648) were submitted to the GenBank. Commercial ripe peaches with the size of about 15 cm × 15 cm × 10 cm was used for pathogenicity test. Peaches were surface disinfected with 75% ethanol, then a wound with 4 mm in diameter and 5 mm in depth was made on the surface of each fruit. Ten peaches were inoculated with 10 μL (1×105 spores /mL) of the isolate suspension. Another ten peaches were inoculated with 10 μL sterile water as the control. Peaches were incubated individually at 28 ℃and a relative humidity of about 85%. After three days, large scale of pits and necrosis appeared on every peach inoculated, and the symptoms were consistent with the diseased peaches in Yangshan Town, while no symptoms non-inoculated on the control peaches were observed. The pathogen was re-isolated from the diseased fruit and was identified again by sequencing of ITS and SSU. All the tests were conducted three times. Considering the evidence, we identified the pathogen as G. candidum. This pathogen has been reported to cause sour rot was reported in kiwifruit, strawberry, melon and other fruits (Alonzo et al. 2020; Cheng et al. 2020; Halfeld-Vieira et al. 2020). To our knowledge, this is the first report of G. candidum causing sour rot of peach in China, which may cause a great loss to peach industry of China.

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